Idiopathic dilated cardiomyopathy (IDC), resulting in an enlarged heart that does not pump properly, is a common disease (~ 1:2500) associated with an annual mortality rate of greater than 10000 deaths. These statistics underscore the significance for developing new therapeutic strategies aimed at understanding, preventing, arresting or reversing progressive cardiac dysfunction. However, to date, the cause(s) of IDC is (are) unclear and the molecular signaling mechanisms that are aberrantly regulated in IDC are largely unknown. Our proposal will determine whether aberrant regulation of the small GTPase RhoA by the protein tyrosine phosphatase Shp2 is directly involved in mediating IDC pathogenesis. Our recently published work shows that hearts from mice with cardiomyocyte-specific deletion of Shp2, a key positive regulator in most, if not all, receptor tyrosine kinase (RTK) signaling pathways, develop a severe dilated cardiomyopathy (DCM). This loss of Shp2 also revealed a hyper-activation in the RhoA signaling pathway, implicating a novel, yet undefined, connection between Shp2 and the RhoA signaling pathway in the heart. We hypothesize that suppression of RhoA activity, via Shp2, is cardioprotective and, as such, is biochemically required to prevent IDC and heart failure. RhoA is a small GTP binding protein involved in important cellular functions including cell proliferation, migration and cytoskeletal reorganization. Recent translational work has demonstrated a significant role for RhoA in cardiovascular disease, including hypertension and atherosclerosis; however, here too, the underlying mechanisms are unclear. In this proposal, we will elucidate the mechanisms by which RhoA is regulated by Shp2. This proposal addresses several interesting and key questions with regards to the function of RhoA in cardiomyocyte disease. Using a combined, comprehensive set of biochemical, cell biological, proteomic and genetic approaches, we plan to (1) determine the physiological significance of loss of RhoA activity in the adult myocardium (2) determine whether loss of RhoA expression and/or activity can rescue the functional cardiac defects in Shp2 deleted mice in vivo, and (3) utilize proteomic and in vitro and ex vivo biochemical approaches to examine the mechanism by which Shp2 regulation of RhoA affects RTK signaling in the myocardium. Results of this proposal will elucidate the mechanism(s) by which RhoA activity is regulated in the adult myocardium, reveal the manner in which Shp2 regulation of RhoA activity may be cardioprotective, and assist in the generation of novel, molecular-based pharmacological targets for the treatment of heart failure in patients with IDC.